pkone
Posts: 24
Joined: Fri Dec 05, 2003 10:25 pm

Why Not Design Planes To Fly Higher?

Fri Dec 05, 2003 10:44 pm

Hey folks,

First post and I apologise if this has already been covered. I was just wondering why they do not design the average commercial plane to fly at +40,000ft ('above the weather')...several of the high end private planes can do this as did the concorde obviously...its just that turbulence bothers me and many others, I know.

Tks.

Pk
 
goboeing
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RE: Why Not Design Planes To Fly Higher?

Fri Dec 05, 2003 10:47 pm

The tropopause starts at 25,000 to 50 some thousand feet, depending on the time of year and location on earth. At this layer of the atmosphere, the temperatures stop cooling with altitude and stabilize and actually warm up again. Flying in warmer, less dense air makes it hard for a plane to fly. I'm sure there's other reasons too; this may not be the main one, but it must be a factor.

Nick
 
zionstrat
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RE: Why Not Design Planes To Fly Higher?

Fri Dec 05, 2003 11:38 pm

The prime reason is the decrease in air pressure. At 40k, your body can handle rapid decompression, and an emergency decent gets you back into breathable air within minutes- At higher altitudes your blood actually boils, so short of multiple failsafe measures (multi-hulls for examples) or space suits, very high flight is simply not safe.

Once the turbine/ ram/scram/ jet issues get solved, this remains one of the bigger challenges to a suborbital, atmosphere skipping or orbital commercial design. Of course the military is willing to assume these risks and will get there first.
 
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Richard28
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RE: Why Not Design Planes To Fly Higher?

Sat Dec 06, 2003 12:58 am

Zionstrat is right on this one, current jet engines need oxygen to make their engines work. The lower the pressure, the less the oxygen, the harder it is for your average jet turbine engine to function efficently.

Concorde did not use turbine engines, and was more like a rocket in its operation, so it could fly without these problems - but at the cost of fuel efficency - and ticket prices!

A scram engine is one that is able to work in both high and low levels of air pressure - and IIRC the Nasa "Venture Star" project (replacement space shuttle) was exploring these difficult areas.

Rich.
 
Accidentally
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RE: Why Not Design Planes To Fly Higher?

Sat Dec 06, 2003 1:19 am

Concorde did not use turbine engines

Which Concorde would that be?
Indianapolis, IN
 
learjet25
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RE: Why Not Design Planes To Fly Higher?

Sat Dec 06, 2003 1:25 am

20 series Lears go up there all the time and rarely cost over 1 million
 
zionstrat
Posts: 225
Joined: Sat Apr 28, 2001 3:26 am

RE: Why Not Design Planes To Fly Higher?

Sat Dec 06, 2003 1:51 am

Lears are small cabins, which makes them easier to pressurize than commercial size- But even with only 10k feet difference, there are major risks at this height:

1. You're on the edge of not being able to sustain mask pressure- Only forced air military type masks can keep this up for anytime-

2. There's no time to deal with the problem- As a result, one pilot is always on gas at these heights, and the safty margin is lower.

3. Even thought it's easier to make small structures more failsafe, almost any pressurization failure will be explosive because the cabin vol will be so low in proportion to the leak.

Again, going higher and bigger is very difficult.
 
lehpron
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RE: Why Not Design Planes To Fly Higher?

Sat Dec 06, 2003 2:10 am

"Concorde did not use turbine engines, and was more like a rocket in its operation, so it could fly without these problems - but at the cost of fuel efficency - and ticket prices!"

Uh, dude, I think you need to recheck your sources on that one. She had afterburning turbojets, like a fighter plane. I hope you are not assuming rocket just because there as a bright flame coming out the back of those engines....

As for higher, think of this: the total surface area of the fuselage of a bizjet is small compared to the total area of an airliner with respect to the stress that their fuselages can take. With the same material, a smaller plane will fly higher than a larger plane of a very specific design. That is my guess.

Cuz when you go higher up the air pressure drops like a brick, as it will drop about 10 times per 10 miles up. Therefore, at 20 miles it is 100 times less than sea level and so on.

Certain wing designs need lift and may not be able to stay in the sky it the air is too thin and it is just as well with certain engines. Thinner the air less thrust, less thrust means it will go slower until it stalls way up there, which is not good. The faster you go the less thin air seems, this is evident if you stick out hand out the window of a car at different speeds, it feels thicker when you are faster. For Concorde's wing design, it has to go above Mach just to keep from stalling way up there at FL600.

Here is a thought: NASA's pathfinder plane by Aerovironment is a solar electric airplane that flies at 20kts and at FL1000, it has a light wing loading and thick wing cross section. Rather contradicts would you would normally think, huh?


Uh, don't confuse the guy with suborbital altitudes, I think he'll assume space flight after that ignorant Concorde comment.
The meaning of life is curiosity; we were put on this planet to explore opportunities.
 
InnocuousFox
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RE: Why Not Design Planes To Fly Higher?

Sat Dec 06, 2003 2:21 am

Also, if you think 40,000 is "above the weather" you haven't been in the Midwest during thunderstorm season.
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